VAMP 259 - Earth-Fault Distance Protection Ze< (21 N)

Technical description
2 Protection functions
2.4 Distance protection Z<
VM259.EN007
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57
2.4.2. Earth-fault distance protection Ze< (21N)
The earth-fault distance protection function calculates the
impedance
 
00
3 IkI
U
Z
G


of the earth-fault fault loops.
K
0
= (Z
0L
– Z
1L
) / (3 x Z
1L
)
Z
0L
= Zero sequence line impedance
Z
1L
= Positive sequence line impedance
If impedance is inside the tripping zone (normally presented in
R-X plane) and set I
0
current is exceeded, the distance function
operates. In earth-fault faults there are 3 possible fault loops.
The VAMP distance protection function calculates the
impedances of the fault loops continuously and thus separate
pick-up conditions are not needed.
Figure 2.4.2-1 An example of tripping zone. Gray area is the tripping zone,
polygonal characteristics.
Figure 2.4.2-2 Earth-fault fault loops.